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NMTA 40 vs CAT 40

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Gordon

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My mill has a NMTA 40 taper. Recently I had reason to use a CAT 40 holder. The basic taper is the same and they both have 5/8-11 threads but the NTMA is about 3/4" longer and the CAT has a pull stud. I solved the problem by making a longer draw bar but I do not understand how the pull stud works. Is there a way that I can make a draw bar which would work on both? At this point I can put a 3/4" long spacer on the draw bar but that involves removing the draw bar and threading it through the hole in the low ceiling. Do not move the mill unless you want to drill another hole in the ceiling. How does the pull stud work? I can find pictures and dimensions of them but I do not know how they work.

Used CAT 40 tooling is much easier to find than NTMA 40 tooling.

Gordon
 

kvom

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Pull studs are locked by hydraulics on CNC mills.

A spacer with a vertical slot would allow it to be removed as needed. You'd need to determine if it would be too unbalanced when spinning.
 

Gordon

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Pull studs are locked by hydraulics on CNC mills.

A spacer with a vertical slot would allow it to be removed as needed. You'd need to determine if it would be too unbalanced when spinning.
Thanks. At this point I have two draw bars of different length. The problem with a slotted spacer is that the spacer must be attached to the draw bar so that it does not end up in the bottom of the hole in the mill where it would be difficult to remove. If it remained down in the bottom of the hole it would require a magnet to get it back out.
 

Chiptosser

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A lot of the current mills, lower priced, no hydraulic's, use bellville springs to retain the knob. The springs are combined (stacked) to pull the tool holder into the spindle,by the stud. A clam shell type of gripper pulls the stud.
I think, you would have to weld a spacer.
 

L98fiero

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Pull studs are locked by hydraulics on CNC mills.

A spacer with a vertical slot would allow it to be removed as needed. You'd need to determine if it would be too unbalanced when spinning.
I stand to be corrected but every Cat or BT machine I have seen uses a stack of Bellville washers to pull the stud in and uses air to release it. The cylinder is separate from the spindle and just pushes on the drawbar, the idea is that they don't need a high speed hydraulic/air fitting to hold the pressure on the drawbar.
 

Gordon

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Thanks for the information. That answered my question as to whether it was possible to make a drawbar to fit in my mill which would use the pull stud on a CAT 40 holder. My two different length draw bars or one with a spacer is the only answer. I was hoping for a simple universal solution
 

rmd55

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My draw bar for my K&T, uses 50 taper, has a threaded section and a nut at the rear of the draw bar. There is also a fixed nut pinned at the very end of the bar. This allows me to use NMTB, CAT50, or 40 taper tooling with adapter. The draw bar also has 1in and 5/8in threads on the pull end. Factory design from K&T.
Richard
 

Gordon

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My draw bar for my K&T, uses 50 taper, has a threaded section and a nut at the rear of the draw bar. There is also a fixed nut pinned at the very end of the bar. This allows me to use NMTB, CAT50, or 40 taper tooling with adapter. The draw bar also has 1in and 5/8in threads on the pull end. Factory design from K&T.
Richard
Thanks. I did a search for K&T drawbar and that looks like I could actually make something similar to work in my machine. What keeps the bottom adjustment nut in place when it is in the machine? I would assume something like a set screw or something like nylock threads. Without some way to keep the adjustment nut from turning it would soon be out of adjutment.

Gordon
 

rmd55

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Gordon,
You hold the pinned nut and tighten the "adjustment" nut to pull the tools in. No adjustment needed.
Richard
 

Gordon

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Gordon,
You hold the pinned nut and tighten the "adjustment" nut to pull the tools in. No adjustment needed.
Richard
OK that makes sense. On my mill the contact surface for the nut is buried about 2" down inside the spindle so that is not accessible from the top unless you made the bottom nut about 2 1/2" long. Obviously on your mill both nuts are exposed.

Gordon
 

rmd55

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You could do that but just thread the top 1/2in or so. The nut on the K&T I have is about twice as long as a standard 1in nut only about 1/2 of it is hex to fit down inside not as far as yours bout the same idea.
Richard
 

Kevinb71

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Don't want to hijack the thread, but Richard could you post a picture of that drawbar? Thanks
 

Gordon

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Here is what I found. Explained it to me.
1603374183413.png
 

rmd55

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Thanks Gordon I am i the process of moving. Had to move into an apartment while looking for the right house, with shop space and the wife approves. My machines are storage a 1000 miles away. there is a local maker space that I need to look into as soon as things get unpacked.
Richard
 

MisterFixIt1952

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There are quite a few videos on youtube about retrofitting a power drawbar to a mill, the belville stack being the most popular. I just bought a used Denford Triton Pro CNC machine with an auto tool change BT30 spindle which uses a belville stack for the drawbar on the ATC (Automatic Tool Changer).
Here is the spindle mechanism on my mill. Variations of this ATC are fairly easy to adapt to almost any spindle
Novamill-Milling-Head-ATC-RM6-100.jpg

Try this youtube video for some good information.
 

Gordon

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Thanks to all of you. It is pretty obvious to me that I am not going to do a lot of modification to my drawbar. In my home shop tool changes are just not that frequent so some inconvenience is not really a significant problem. Most changes involve just changing the collet from 3/8 dia to 1/2 dia and sometimes installing a drill chuck. Changing the collet does not require removing the holder. I am sure that by the end of the month a quick change drawbar would save less than an hour.

Gordon
 
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